The term "electrostatic discharge" refers to the transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact. The International Electrotechnical Commission (IEC), Bellcore and others have promulgated standards, which relate to the immunity requirements and test methods for electrical and electronic equipment subjected to electrostatic discharges from operators directly and, from adjacent objects. See "Electrostatic Immunity Discharge Test", International Standard IEC 1000-4-2(1st Ed. 1995); IEC 801-2 (2nd Ed. 1991). The object of these standards is to establish a common and reproducible basis for evaluating the performance of electrical and electronic equipment when subjected to electrostatic discharges.
The principal tool for testing a system's compliance with the foregoing standards is an electrostatic discharge ("ESC") generator or, what is known in the art as, an "ESD Gun." An ESD gun generates high voltages/currents and, is used to discharge electrostatic energy directly into the system being tested. The gun is built in accordance with IEC specifications and accordingly, the gun's discharge model contains the timing characteristics (e.g. the waveshape of the discharge current) specified by the IEC. The ability of a system under test to perform without degradation, whether temporary or permanent, in the presence of the ESD disturbance is used in assessing the system's ESD susceptibility. A degradation in performance can range from a transient malfunction of the system to the damage of components therein.
System tests for ESD susceptibility are performed using measurable performance criteria. Such criteria includes testing under a particular system configuration (e.g. the system at a particular stage in development is one system configuration and, the system as delivered to the customer is another; each would have its own ESD susceptibility characteristics), climatic condition (e.g. low relative humidity), and level of ESD intensity. Moreover, testing is designed to match a variety of electrical conductivities including that of an operator and that of adjacent objects. In this regard, both contact tests and air tests are used, although contact tests are typically favored. During a contact test, the gun is held in contact with the system under test. During an air test, an arc gap is introduced between the gun and the system.
Although the ESD gun is very useful in approximating the real ESD phenomena at the macroscopic level (i.e. determining whether the system as a whole is compliant with IEC standards), the gun does not provide much in the way of fault isolation. This is primarily because the gun's discharge affects a large section of the system simultaneously. As such, lab personnel assigned the task of pinpointing system weaknesses currently have no convenient way of doing so. Their task involves determining whether a system's failure was the result of a single ESD susceptible component or a plurality of such components. When multiple sources of ESD susceptibility exist, each must be identified and ESD hardened before there can be any macroscopic improvement in performance. As one would expect, the larger the system being tested, the more difficult it becomes to isolate each of the ESD susceptible components therein.
Moreover, the use of additional test equipment, such as an oscilloscope, to localize ESD susceptible components is typically not feasible because the scope's probes, when introduced into the system, alter the ESD susceptibility of the components therein. As expected, this can easily lead to an erroneous success (or failure) indication during fault isolation attempts.
Once localized, ESD susceptibility can usually be modified and retested successfully. Accordingly, there is a need for an apparatus that is effective in finding ESD susceptible "hotspots" in systems that have failed conventional ESD testing. These "hotspots" can be major contributors to overall ESD susceptibility problems in the system. Such an apparatus, while facilitating the detection of ESD susceptible components, would decrease engineering man-hours and time to market for ESD immune products.